Previously known drilling equipment is described in Finnish Application No. 891706, in which drilling is carried out either by means of a hammering or a rotating tool. The application describes how a hammer furnished with a drill bit and with or without a bit-rotating tool can be backed into its cylinders if the drilling unit is driven too far forward.
The pressure shocks caused by the tool upon drilling are a disadvantage of the above solution, because they disturb the control of backing the whole tool unit. Generally, it is possible to control the backing of the tool only when the drill head is driven on the wall which is being drilled and detection of the whole drill head reading the target is possible as a result of the backing of the tool.